This invention relates to wireless communications systems and methods, and more particularly, to satellite communications systems and methods.
Satellite communications systems and methods are widely used for voice and data communications. Satellite communications systems and methods generally employ at least one space-based component, such as one or more satellites, that is configured to wirelessly communicate with terminals.
A satellite communications system or method may utilize a single radiation pattern (antenna beam), such as a “global” beam, covering an entire area (footprint) served by the system. Alternatively, in cellular satellite communications systems and methods, multiple radiation patterns (antenna beams, or spot beams) are provided, each of which can serve distinct geographic areas in the overall service region of a satellite system, to collectively serve an overall satellite system footprint. Thus, a cellular architecture similar to that used in conventional terrestrial cellular/PCS communications systems and methods can be implemented in cellular satellite-based systems and methods. The satellite (space segment) typically communicates with terminals over a bidirectional communications pathway, with radio communication signals being communicated from the satellite to a terminal over a downlink or forward link, and from the terminal to the satellite over an uplink or return link.
As is well known to those having skill in the art, terrestrial networks can enhance satellite communications system availability, efficiency and/or economic viability by terrestrially reusing and/or re-radiating at least some of the frequency bands that are allocated to and/or radiated by the satellite communications system. In particular, it is known that it may be difficult for satellite communications systems to reliably serve densely populated areas, because the satellite signal may be blocked by high-rise structures and/or may not penetrate into buildings. As a result, the satellite band spectrum may be underutilized or unutilized in such areas. The use of terrestrial retransmission techniques of at least some of the satellite band frequencies can reduce or eliminate this problem.
Moreover, the capacity of a system comprising satellite and terrestrial retransmission of at least some of the satellite band frequencies can be increased significantly, relative to a corresponding satellite-only system, since terrestrial frequency reuse can be much denser (compact) than that of a satellite-only system. In fact, capacity may be enhanced where it may be mostly needed, i.e., in densely populated urban/industrial/commercial areas. As a result, the overall (hybrid) system may become more economically viable, as it may be able to serve a much larger subscriber base. Finally, terminals for a satellite communications system having a terrestrial component within the same satellite frequency band and using substantially the same air interface for both terrestrial and satellite communications can be more cost effective and/or aesthetically appealing. Conventional dual band/dual mode alternatives, such as the well known Thuraya, Iridium and/or Globalstar dual mode satellite/terrestrial radiotelephone systems, may duplicate some components, which may lead to increased cost, size and/or weight of the radiotelephone.
U.S. Pat. No. 6,684,057, to coinventor Karabinis, and entitled Systems and Methods for Terrestrial Reuse of Cellular Satellite Frequency Spectrum, the disclosure of which is hereby incorporated herein by reference in its entirety as if set forth fully herein, describes that a satellite communications frequency can be reused terrestrially by an ancillary terrestrial network even within the same satellite cell, using interference cancellation techniques. United States Patent Application Publication 2003/0153267 (U.S. patent application Ser. No. 10/151,567, filed May 20, 2002) describes a satellite communications system that includes a terrestrial terminal interface subsystem, e.g., a terrestrial base station, operative to communicate with a satellite gateway via a communications satellite using a first radio interface and to communicate with wireless terminals over a geographic area using a second radio interface.